Recently waste water treatment has increasingly become an important problem. Especially, waste water containing a large amount of lipid such as waste water from the kitchen of a hotel or a restaurant cannot be flushed down the drain as it is, and it is the rule that the lipid concentration is to be reduced to not more than 30 mg/1 as the concentration of the n-hexane extract before flushing the waste water down the drain.
Such lipid-containing waste water is conventionally treated by removing the oil content by a physiochemical pretreatment using a grease trap, a fat splitting tank, a floatation equipment or the like, or a biological treatment before the waste water is flushed down the drain.
Such a physiochemical pretreatment, however, suffers from problems that it requires a facility having a large area and that the cost of building the treatment facility and the cost of disposing the waste oil are very high. In addition, it is necessary that the separated lipid is finally disposed by incineration, dumping, reclamation or the like. Incineration offers a problem of air pollution or the like, and dumping and reclamation are faced with a problem of dump shortage. That is, the disposal of the separated lipid has been difficult.
A method of treating waste water cleanly without the need for separating lipid is therefore in demand.
Application of a method purifying lipid-containing waste water with a microorganism is expected as a method of directly treating the lipid cleanly without producing an air-polluting matter or other harmful matters.
As a matter of fact, however, the activated sludge process cannot be said satisfactory, because it cannot assimilate the lipid and it requires a new facility. Although some strains of yeasts having lipid-assimilating property grow into a globular yeast, they float in a treatment tank and easily flow out. On the other hand, if a conventional method of fixing a yeast with sodium argininate or carrageenan is adopted in order to prevent the yeast from flowing out, the treating capacity is greatly reduced.